This invention relates generally to a system for delivering compressed gas to a receiving tank or vessel and more specifically to a diagnostic method and apparatus for shutting off the gas supply to the vessel if, during the fill cycle, the pressure of the gas in the vessel deviates by an undesired amount from the intended pressure at a desired ramp rate (i.e., desired pressure increase in the fueling hose or line per unit time during the fill cycle). The desire ramp rate directly relates to the desired fill rate.
Numerous supply systems employed to fill a receiving tank or vessel with compressed gas are known in the art. These systems include cascade filling processes and systems that employ multiple high-pressure storage vessels to charge a lower pressure-receiving vessel or tank, as exemplified in Borck U.S. Pat. No. 6,779,568. The '568 patent discloses that, for a constant filling time, the peak temperature of the gas in the receiving tank will be lower when a lower pressure storage vessel is used first during the cascade filling process. Thus, the '568 patent teaches controlling the order in which the storage vessels are utilized based on the difference in pressure within those vessels.
It is also known that the temperature rise in a receiving tank can be limited by adjusting the filling rate, especially at the start of the filling process when the rate of temperature increase is the greatest, as exemplified by the teachings in Hwang, et al. U.S. Pat. No. 5,901,748 and Togasawa, et al. U.S. Pat. No. 6,598,624.
The above identified patents are only representative of the many types of gas supply systems disclosed in the prior art for filling a receiving tank or vessel.
It is highly desirable, and indeed very important that the flow rate of gas into the receiving tank or vessel be controlled to prevent overheating of the vessel. In addition, it is desirable to maintain the flow rate at a sufficient level to prevent an excessively long fill time; a situation adverse to the public adoption of gaseous vehicle fueling.
Thus, the operation of filling a receiving tank or vessel with compressed gas is a process in which the mass of gas directed into the tank or vessel and the total time for filling the tank or vessel should be optimized, as these latter variables impact on the instantaneous pressure and temperature in the receiving tank. If the filling rate is too high, the receiving tank can overheat. Overheating occurs as a result of both adiabatic compression of the gas, and, when the gas is hydrogen or helium, by the reverse Joule-Thompson effect. The heat of compression is partially offset by the isentropic expansion cooling within the storage vessel. Moreover, for gases other than hydrogen and helium, a conventional Joule-Thompson effect takes place, which can further mitigate against overheating resulting from the impact of adiabatic compression of the gas in the receiving tank. However, even when charging a receiving tank or vessel with gases other than hydrogen and helium, the adiabatic compression of gas in the receiving tank creates an overheating concern, thereby requiring that the fill rate be carefully controlled.
The control of the filling operation is complicated when the receiving tank or vessel does not include any instrumentation to provide data on instantaneous pressure and temperature of the gas within the tank or vessel. Under these circumstances, one approach to controlling the fill rate has been to adjust the filling rate based upon the ambient temperature, by actuating one or more control valves to regulate the flow rate of gas to the receiving tank. As shown in FIG. 5 of U.S. Pat. No. 6,786,245, assigned to the same assignee as the instant application, a programmable logic controller (PLC) can take information on pressure (from the supply hose, which indirectly measures or reflects the pressure in the receiving tank) and on ambient temperature, and then regulate the set rate of the programmable pressure regulator using a current/pressure (I/P) controller. Although this system can provide its intended function, the potential exists for malfunctions associated with the control valve, the PLC and/or the I/P controller. For example, the pressure regulator could fail to open the required amount to establish a desired fill rate, thereby resulting in a longer fill time than is desired to achieve the desired pressure in the receiving tank. More significantly, the control valve could also open more than the required amount, thereby creating an excessively high fill rate, creating an unsafe condition due to an excessive temperature rise within the receiving tank. Since the system disclosed in the '245 patent does not include any feedback loop from the receiving tank, the above and other malfunctions in the supply system can go undetected.
U.S. Patent Application 2004/0163731, assigned to the same assignee as the instant application, discloses a gas filling system, but without the ability to monitor the fill rate in relation to set limits and to discontinue the filling operation if the fill rate is outside of the preset limits.
In the loading of compressed natural gas (CNG), U.S. Pat. No. 5,238,030 discloses the action taken by a fueling system when the time variation of the outlet pressure exceeds a certain predetermined limit, which would indicate a “sudden” loss of outlet pressure (e.g., due to the rupture of the dispensing hose).
U.S. Pat. No. 5,029,622 describes a CNG fueling system, including alterations to the operating state of the system when the pressure measurement deviates from a set value; that deviation being determined based upon a change in ambient temperature.
In summary, a number of supply systems include various devices and techniques for controlling the fill rate of gas into a receiving tank or vessel. However, until the present invention, there has not been an effective way for detecting a malfunction resulting in an unacceptably fast or unacceptably slow fill rate without the use of feedback instrumentation on the receiving tank. As is discussed in detail hereinafter, the present invention employs a self diagnostic method and apparatus for detecting when the fill rate is outside of a desired range, thereby signaling a possible malfunction of the supply system and shutting off the gas supply to the receiving tank when such a condition is detected.